1. Field of the Invention
The present invention relates to a reciprocating compressor, and particularly, to an apparatus for controlling an operation of a reciprocating compressor.
2. Description of the Prior Art
In general, by eliminating the use of a crankshaft for converting a rotary motion into a reciprocating motion, a reciprocating motor compressor has a low frictional loss, and accordingly the reciprocating motor compressor is superior to a general compressor in the compressing efficiency aspect.
When the reciprocating compressor is used for a refrigerator or an air conditioner, a compression ratio of the reciprocating compressor is varied as varying a stroke voltage inputted to the reciprocating compressor, thereby controlling cooling capacity. A reciprocating compressor in accordance with the conventional art will now be described with reference to FIG. 1.
FIG. 1 is a block diagram showing a structure of an apparatus for controlling an operation of a reciprocating compressor in accordance with the conventional art.
As shown therein, the apparatus for controlling an operation of the reciprocating compressor includes: a voltage detecting unit 14 for detecting a voltage applied to the reciprocating compressor 13 according to the variation of a stroke of the reciprocating compressor; a current detecting unit 12 for detecting a current applied to the reciprocating compressor 13 according to the variation of the stroke; a microcomputer 15 for calculating a stroke based on a voltage value detected by the voltage detecting unit 14 and a current value detected by the current detecting unit 12, comparing the calculated stroke and a stroke reference value, and generating a switching control signal according to the comparison result; and a power supply unit 11 for supplying a stroke voltage to the reciprocating compressor 13 by on-off controlling the supply of AC power to the reciprocating motor compressor 13 with a triac Tr1 controlled by the switching control signal generated by the micro-computer 15. Herein, the reciprocating compressor 13 receives a stroke voltage supplied to an internal motor (not shown), varies a stroke according to a stroke reference value set by a user, and thereby vertically moves an internal piston (not shown).
Hereinafter, operations of the apparatus for controlling an operation of a reciprocating compressor in accordance with the present invention will now be described.
First, the reciprocating compressor 13 receives a voltage supplied to the internal motor, varies the stroke according to the stroke reference value, and moves the piston vertically according to the varied stroke. Herein, the stroke means a distance over which the piston inside the reciprocating compressor 13 moves while reciprocating.
A turn-on period of a triac (Tr1) of the power supply unit 11 is lengthened by a switching control signal outputted from the microcomputer 15, and the AC power is supplied to the reciprocating compressor 13 due to the lengthened turn-on period, so that the reciprocating compressor 31 is driven. At this time, the voltage detecting unit 14 and the current detecting unit 12 detect a voltage and a current which are applied to the reciprocating compressor 13, and output the detected voltage value and the detected current value, respectively.
The microcomputer 15 calculates the stroke based on the voltage value and the current value respectively detected by the voltage detecting unit 14 and the current detecting unit 12, compares the calculated stroke with the stroke reference value, and generates a switching control signal according to the comparison result. For example, if the calculated stroke is smaller than the stroke reference value, the microcomputer 15 outputs a switching control signal for lengthening a turn-on period of the triac Tr1 to the power supply unit 11, to increase a stroke value to be supplied to the reciprocating compressor 13.
On the other hand, if the calculated stroke is greater than the stroke reference value, the microcomputer 15 outputs a switching control signal for shortening a turn-on period of the triac (Tr1) to the power supply unit 11, to decrease a stroke voltage to be supplied to the reciprocating compressor 13.
A capacitor (C) that is connected to an internal motor of the reciprocating compressor 13 in series, countervails an inductance of a coil wound in the internal motor. That is, since an inductance of the coil is countervailed by the capacitor (C), sufficient stroke is generated even with a lower input voltage. However, when power is supplied to the internal motor of the reciprocating compressor at an initial stage, an overcurrent is generated, thereby causing a damage of the reciprocating compressor.
Hereinafter, a PTC thermistor (Positive Temperature Coefficient Thermistor) which is added to an apparatus for controlling an operation of a reciprocating compressor in accordance with the conventional art in order to prevent a damage of the reciprocating compressor will now be described with reference to FIG. 2.
FIG. 2 is a block diagram showing a PTC thermistor (Positive Temperature Coefficient Thermistor) which is applied to the apparatus for controlling an operation of a reciprocating compressor of FIG. 1
As shown therein, the PCT thermistor is connected to the capacitor (C) in parallel and cuts off an overcurrent generated when the reciprocating compressor 13 is initiated at an initial stage, thereby preventing a damage of the reciprocating compressor 13. For example, when the compressor 13 is initiated at an initial stage, the PTC thermistor cuts off an overcurrent applied to the internal motor of the compressor, thereby protecting the compressor 13 from being overloaded. Herein, the overcurrent means a current greater than a reference current value the inner motor (M) of the reciprocating compressor 13 allows.
In addition, when a resistance value of the PTC thermistor is increased by a current applied to the internal motor (M) of the reciprocating compressor 13, the PTC thermistor becomes off. Then, the current is applied to the internal motor only through the capacitor (C).
Hereinafter, a wave form of a stroke when the reciprocating compressor operates, will now be described with reference to FIG. 3.
FIG. 3 is a view showing a stroke wave form when a reciprocating compressor in accordance with the conventional art operates.
As shown therein, when power is applied to an internal motor (M) of the reciprocating compressor through the PTC thermistor at an initial stage, an overcurrent and a surge current are generated, and an overstroke (A) (a stroke more than a reference value) is generated by the surge current. That is, a piston and a discharge value collide with each other by the surge current, thereby causing a damage of the reciprocating compressor, and by this collision is increased a noise of the reciprocating compressor. Herein, the surge current means a maximum current of a current exceeding a reference current value the internal motor (M) allows. That is, overcurrent is mostly cut off through the PTC thermistor, but still the surge current is applied to the internal motor (M).
A reciprocating compressor in accordance with a different embodiment of the present invention is disclosed in U.S. Pat. No. 6,644,943 registered on Nov. 11 in 2003.